Which drug schedules need to be kept separate from all other substances?

The correct choice highlights the important regulations governing controlled substances, particularly those categorized as Schedule I and II drugs. These drugs are placed in these schedules due to their high potential for abuse, dependence, and their lack of accepted medical use (in the case of Schedule I) or their accepted medical use but with severe restrictions (in the case of Schedule II).

Schedule I substances are considered the most dangerous, and as such, they are strictly controlled and must be stored and handled with the utmost care. Schedule II substances also require careful management, but they are recognized for medical use. Because of the significant risks associated with abuse and diversion, both Schedule I and II substances must be kept separate from all other drugs. This separation is crucial for ensuring compliance with regulations and for protecting public health.

The other schedules, such as III, IV, and V, have lower potential for abuse and different regulatory requirements, which allows them to be managed alongside less controlled substances. Therefore, the correct answer reflects the strict regulations that apply specifically to the handling and storage of Schedule I and II drugs.